Refractive surgery Flashcards
when shouldn’t u have refractive surgery
unstable ametropia only 1 seeing eye irregular corneal surface viral infections pregnancy drugs/steroids which affect healing response inappropriately motivated
What does px need to do for the initial assessment
leave out cl RG- a month soft- 2 weeks Bring in ur past RX's to show stability asses px's expectations
What do u check pre-surgery
Visual function- Va- Rx- cyclo? fields Fundus examination Anterior examination IOP CONSENT pupil diameter pachymetry biometry corneal topography tear film quality aesthesiometry- corneal sensitivity muscle balance amp of accom
What base do u need when correcting on cornea
Myopes need BASE IN
Hyperopes get BASE OUT
What’s the relative contact lens magnification
CLM- 1- d*Fsp
What happens to IOP levels after surgery
After myopic laser surgery- IOP reduced
after corneal grafts- increased
NOT the actual IOP measurement but due to the
What’s keratoplasty
Corneal graft
Could be full- penetrating
or partial
A donor cornea is used when host tissue is diseased. Sutured up.
Lamellar Refractive Keratoplasty
can either have
keratophakia- donar/synthetic lens for cataract px
keratomileusis- slicing into cornea then reshaping it- for myopic px
epikeratoplasty- donor cornea- epithelium grows over graft to correct hyperopia
What’s keratectomy
TO CORRECT ASTIGMATISM remove tissue crescent piece of corns cut residual sutured steepening in that meridian Photorefractivfe keratectomy- light energy used to remove tissue
What’s keratotomy
cutting into cornea incisions not on visual axis obis cornea can be weak due to this trauma may cause a globe rupture 2 types: RK radial patterns for spherical correction- flattening cornea and AK astigmatic keratotomy where transverse patterns for astigmatism cut
what’s thermal kerotoplasty
the remoulding of the cornea
heating probe applied in mid- peripheral cornea-
localised shrinkage go collagen- therefore central steepening- hyperopia
can use Nichrome (NiCr) wires- 600degrees for 0.3secs-probs include unstable rx, recurrent erosions, scars, necrosis, vascularisation or YAG Holmium laser at 60degrees or even conductive keratoplasty- which use radio waves at 65degrees for 0.6seconds.
what do u do to each refractive error in refractive surgery
myopes- flatten- ablate- remove tissue
hyperopes- ablate mid-peripheral- which steepens- u have changed contour
whats an excimer laser
EXcided dIMER
Cold laser- vaporise tissue
Breaks molecular binds in cornea- initially KrF-248 now ArF-193nm.
initially for computers.
first used for keratotomy X didn’t work as u ablated tissue. so used in photo refractive keratectomy then lasik/ lasek
tell me about PRK
insert speculum put anaesthetic get them to look at a target then u remove epithelium with either alcohol/manual blade? or even a mechanical rotary brush this weakens epithelium dry corneal bed ZAP
Gives u uneven thickness- unpredictable results
after op- re-epithalised and PAIN
antibiotics, steroids?
ocular lubricants?
Va could be poor- stable after 6-12 weeks
what happens in lasek- what faisal has- faisal flap- ff- ffs- ff- flap- lasek
well epithelium is weakened with alcohol also but instead of being removes,
its scraped to one side
then re put over like a sort of bandage
this gives less pain, quicker recovery
whats lasik all aout
insert speculum aneasthetise cornea get them looking at a target then u raise iop with a suction ring warn them vision may go black due to blocking of central retinal artery then create flap with microkeratome dry corneal bed zap with laser then replace flap- less painful and quicker recovery- OCCURS FURTHER INTO CORNEA
does corneal thickness matter in lasik
yes- needs to have a safe bed- approx half corneal thickness- 200um
u usually cut a flap of 160um
abblation depth calculation depends on munnerlyn formula. Wider diameter- u need to cut deeper - too deep- ecstasia
t = -(S2 x D) / 8(n-1)
whats diffuse lamella keratitis
between flap and stromalbed- infection- photophobia, vision loss, blephorpasm, give antibiotics and wash out flap
problems with lasik
flap truncation flap edge defect MG secretion under flap lamelle keratitis striae epithelial cells epithelial cells at flap edge fibres inflammatory response
complications of PRK
sterile infiltrates ptosis infections haloes glare and then after a while could get regression persistent haze night vision problems irregular topography and recurrent erosions OPACIFICATION?
when would u get haloes
if zone diameter is small than pupil
what are the recent developments in laser
custom ablations iris recognition features eye trackers lasers to now cut flap also multifocal ablations
whats scleral surgery
increases effective working distance of the cilliary muscle with pesbyoia.
radial incisions- to allow CB to shift outwards. silicone implants can be put in cuts- scleral expansion bands
accommodating IOLs
Haptic allows forward movement of optic in response to accommodation
As ciliary body contracts, vitreous cavity pressure rises & IOL optic moves forward Movement causes ↑+ve power
